1. Technical Field
The invention relates to a system for brake lining wear and temperature estimation and more particularly to such a system implemented using extant sensing elements of an air brake system, of an air suspension system, or both.
2. Description of the Problem
Effective brakes are essential to safe motor vehicle operation. Primary brake systems dissipate vehicle kinetic energy through brake friction linings/pads as heat. These brake pads have a relatively short life and require regular replacement. Heavy vehicles have historically exhibited problems with brake overheating and fade, especially when the vehicles are descending along long grades. Overheating reduces stopping ability and accelerates brake pad wear.
Inspection of the brake system has traditionally involved disassembly of the wheel mechanism and visual examination of the pads. It has long been recognized that it would be desirable to incorporate some kind of sensor into the brake pads that monitor wear of the pads without the need to disassemble the brake system. Were the same sensor used to monitor brake temperature the addition to vehicle complexity would be minimized.
Various brake lining wear detection systems and brake temperature measurement systems are known in the art. Indirect wear or temperature estimation systems which minimize, or avoid alteration of the brake system are less usual. In principal, brake wear has been related to three variables in brake operation: (1) the pressure at which the brakes are actuated; (2) the length of time that the brakes are actuated; and (3) the rotational speed of the brake disc or drum relative to the wearable friction elements. These factors were applied in a system for determining lining condition as described in German Laid Open Application DE 34 07 716 A1 to Maurer, et al. The apparatus described by Maurer, et al. provides a pressure sensor and a timer disposed in operational cooperation with at least one of the brake lining installations for a vehicle. The rotational velocity of the disc (or brake drum) is provided by a velocity sensor. Beginning with a new installation of brake linings the signals generated by the various sensors are supplied to a plotting device which in turn generated a wear index (tracking an internal model) for display to the vehicle operator. Estimation of the brake lining wear was indirect, but the system still relied on additional sensors placed in close proximity to the brake lining.
In European Patent Application 0 594 113, temperature calculation was made fully indirect. The signal generated by a pressure sensor such as might be placed on a brake control valve was used as an indicator of brake pressure. This signal and a speedometer signal were used as inputs to an incremental brake temperature calculation algorithm as long as the signal of the pressure sensor was high. Brake temperature was incrementally decremented when the pressure sensor signal indicated that the brake was off. The algorithm operated cyclically.